Acoustic monitoring of parts for incipient failure is industrially well known and has been used for bridges, nuclear power plants and aircraft. Typically, the acoustic equipment is configured with an acoustic emission sensor electrically hard-wire connected to a controller.
Monitoring of cutters for cutter breakage is also well known and used especially for rotary cutters on machine tools, for example milling machines, drills, saws, and rotary shears. For example, U.S. Pat. No. 4,636,779, ACOUSTIC DETECTION OF TOOL BREAK EVENTS IN MACHINE TOOL OPERATIONS, uses an accelerometer to detect tool breaks.
U.S. Pat. No. 4,918,616, TOOL MONITORING SYSTEM uses an acoustic emission sensing unit for detecting a tool failure in a tool machine. In this system, an artificial signal generating unit generates a predetermined artificial tool failure signal simulating the acoustic emission signal obtained in an actual failure of the tool for comparison to actual acoustic emission received during operation of the tool. When the actual acoustic emission matches the artificial signal, then a tool break is confirmed.
U.S. Pat. No. 4,884,449, APPARATUS FOR DETECTING A FAILURE IN BEARINGS, uses an acoustic emission sensor which detects acoustic emission from a bearing. Signals indicative of power of the acoustic emission are passed through a bandpass filter which passes only signals in the range of from 100 kHz to 500 kHz. A comparator compares the passed signals with a predetermined threshold value and outputs any event signals which exceeds the threshold value. A computer receives the event signals from the comparator, then determines time intervals or duration of the event signals. The number of event signals are counted in each time interval and total count compared to a predetermined threshold count value to determine a failure in the bearing.
U.S. Pat. No. 4,707,687, DETECTOR TO DISCRIMINATE BETWEEN TOOL BREAK ACOUSTIC SIGNATURES AND SPIKY NOISE, recognizes that in some machining conditions the background noise in an acoustic cutting tool break detection system is a low mean level with fairly dense high amplitude noise spikes. A common tool break vibration signature is the sudden appearance of a dense high amplitude (spiky) noise. Digital signal pattern recognition logic uses an up/down counter to reject the noise on the basis of its lower spike density while alarming on such a tool break signature. Preprocessed vibration signal samples are tested against a detection threshold and an alarm generated when amplitudes above the threshold amplitude exceeds a preset count.
In the food processing industry, specifically vegetable processing by cutting, more specifically potato cutting, a self-supporting blade grid has been used. Potatoes are moved past the self-supporting blade grid and sliced as shown in U.S. Pat. No. 5,009,141. An advance in throughput was realized by putting the potatoes in water and pumping the water/potato stream through the self-supporting blade grid as shown in U.S. Pat. No. 3,109,468, and FIG. 1. A pipe 10 carries potatoes 12 into a box or housing 14. The housing 14 contains one or more self supporting blade grid(s) 16 wherein the potatoes 12 are cut into slices 18. Occasionally a foreign object, for example a rock, would be passed with the potatoes to the self-supporting blade grid whereupon the rock would deform the self-supporting blade grid and become trapped therein. Incoming potatoes would stack up behind the rock. By implementing a pressure transducer (not shown) to detect the clog, the pressure transducer provided a signal upon clogging whereupon (see FIG. 2) an actuator (not shown) moves the housing 14 containing a spare blade grid 20 from a clogged position A (indicated by dashed lines) to an unclogged position B thereby diverting potatoes to the spare self-supporting blade grid 20 and taking the first self-supporting blade grid 16 out of service, permitting an operator to remove the deformed and clogged self-supporting blade grid 16 and replace it with a new one.
Yet a further advance was realized upon introducing much thinner blades maintained by tension as described in U.S. Pat. No. 5,343,623 as a tension blade grid having an advantage of less waste. However, with the thin blades only 0.08 inch (0.20 cm) thick, upon being struck by a rock the thin blade would sever rather than deform, the rock would pass and incoming potatoes would not be cut by the severed blade thereby permitting irregular cuts of potatoes to pass the tension blade grid. Further, the thin tension blades are more affected by the varying loads compared to self supporting blades. The varying loads are imposed as vegetables are alternately in contact then no contact with the tension blades thereby creating a time varying stress that leads to fatigue of the tension blades. Thus, even absent a foreign object such as a rock, one or more tension blades may fail by fatigue permitting irregular cuts to pass the tension blade grid. Stationing an inspector to watch the output of the blade grid for irregular cuts is expensive and undesirable.
Accordingly, there is a need in the acoustic emission industry for an apparatus wireless combination of sensor unit and transmit/receive station. Further in the food processing industry, there is a need for a fully reliable detector of a malfunction of a tension blade from which a signal may be used to divert the incoming vegetables, especially potatoes, as was done when using the self-supporting blade grid.